The present invention relates to a rocker arm assembly which includes a bridge which snaps into a rocker arm body and forms oil-transporting channels for transporting oil from one end of the rocker arm body to the other across a trunnion pedestal opening.
A common rocker arm design includes side walls having aligned apertures therethrough for receiving a pivotable trunnion. The opposing ends of the rocker arm are engaged against a push rod and valve stem for transmitting forces therebetween about the rotatable trunnion. Typically, the push rod forces oil into one end of the rocker arm, and the oil is required to flow from that end to the other end for lubricating the rocker arm""s engagement with the valve stem. Typical cast rocker arms include a trough formed along the top of the side walls of the rocker arm for delivering oil from the push rod to the valve stem.
Recent innovative improvements in rocker arm manufacturing and design, such as that described in U.S. Pat. No. 5,887,474 and hereby incorporated by reference, have enabled the cold-forming of one-piece metal rocker arms by devising a method for cold-forming outwardly extending tubular portions in the side walls of the rocker arm. This advancement has significantly reduced manufacturing costs over prior methods, which typically required drilling or piercing of aligned apertures through side walls and installation of a support tube between the apertures. The one-piece cold-formed rocker arm, however, presents a new challenge in delivering oil from the push rod end to the valve stem end of the rocker arm because cold-formed rocker arms cannot be formed with the above-mentioned troughs for carrying oil from one end to the other.
At high engine speeds, oil is sprayed from the push rod into the interior of the rocker arm body and sufficiently lubricates the rocker arm. However, at low engine operating speeds, oil flow is reduced and pools at the push rod end of the rocker arm body. Accordingly, this oil must somehow be transported to the opposite end of the rocker arm body to lubricate the point of engagement of the rocker arm body with the valve stem.
In particular, if the trunnion is narrow in width, the oil cannot simply flow over the top of the trunnion, but must be transported.
One prior art rocker arm assembly includes a rocker arm body with a steel bridge which is spot-welded into the rocker arm body to transport oil from one end of the rocker arm body to the other. This spot welding process is, of course, an expensive operation which adds significant costs to the manufacturing and assembly operation.
Accordingly, the need exists to provide an improved rocker arm design in which oil is transported from one end of the rocker arm body to the other regardless of trunnion size.
It is further desirable that such a rocker arm assembly be compatible with a one-piece cold-formed rocker arm body design and not require spot welding or other additional, expensive manufacturing processes.
The present invention improves upon the above-referenced prior art rocker arm assemblies by providing an oil transporting bridge which is adapted for snap-fit cooperation with a rocker arm body to form oil channels for transporting oil from one end of the rocker arm body to the other end.
More specifically, the present invention provides a rocker arm assembly including a rocker arm body having opposing side walls with annular flanges extending outwardly therefrom and forming aligned bores for receiving a trunnion. The opposing side walls are connected by a bottom wall having separate first and second portions. The first portion is configured to engage a push rod and the second portion is configured to engage a valve stem. The side walls and the first and second portions of the bottom wall cooperate to form an aperture to receive a pedestal for supporting the trunnion. The aperture has first and second edges. A bridge includes first and second tabs protruding from first and second distal ends of the bridge for snap-fit cooperation with the first and second edges, respectively. The bridge is generally semi-circular in side view and has a bridge opening bordered on opposing sides by first and second upstanding lips. The first and second upstanding lips cooperate with the opposing side walls to form first and second oil-transporting channels for transporting oil from the first portion of the bottom wall to the second portion for lubricating the rocker arm body at the point of engagement with the valve stem as the rocker arm body rocks back and forth.
Preferably, the bridge is a stamped spring steel component so that the bridge is sufficiently flexible to allow the first and second distal ends to flex toward each other as the bridge is inserted into the aperture. The bridge also preferably includes first and second flanges extending along lateral edges of the bridge to add structural integrity to the bridge to prevent disengagement of the bridge from the aperture.
The rocker arm assembly includes first and second bearing shells positioned in the aligned bores. The first and second flanges abut the first and second bearing shells so that the bridge is held in position by the engagement of the tabs with the first and second edges and the engagement of the flanges with the first and second bearing shells.
Preferably, the rocker arm body is a one-piece cold-formed metal component. However, with the present invention, the rocker arm body could be cast, or a welded assembly.
Objects, features and advantages of the invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.